Catch comparison of pulse
trawls vessels and a tickler
chain beam trawler
B. van Marlen, J.A.M. Wiegerinck, E. van Os-Koomen, E.
van Barneveld, R.A. Bol, K. Groeneveld, R.R. Nijman1, E.
Buyvoets, C. Vandenberghe, K. Vanhalst 2
Report C122b/11
IMARES
Wageningen UR
(IMARES - Institute for Marine Resources & Ecosystem Studies)
Client:
Ministry of Economic Affairs, Agriculture and Innovation
(EL&I)
Prins Clauslaan 8,
2595 AJ Den Haag
This research is performed within “Beleidsondersteunend
onderzoek (BO)” of EL&I-programs
BAS-code: BO-12.04-001-027
Publication date:
22/11/2011
1 IMARES Fishery, IJmuiden, the Netherlands
2 ILVO Fishery, Ostend, Belgium
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Report number C122b/11
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
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
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Report number C122b/11
Contents
Contents ...................................................................................................................3
Summary..................................................................................................................5
1.
Introduction .....................................................................................................6
2.
Assignment ......................................................................................................6
3.
Materials and Methods .......................................................................................7
Foreign experts ................................................................................................7
Vessels
7
Fishing gears7
Pulse stimulation............................................................................................. 13
Comparative fishing ........................................................................................ 14
Data collection ................................................................................................ 15
Statistical analysis .......................................................................................... 16
Length dependency of results for major target species.......................................... 17
4.
Results .......................................................................................................... 18
Overall performance ........................................................................................ 18
Landings recorded at the auction ....................................................................... 18
Landings and discards raised to total trip duration ............................................... 19
Target fish species ................................................................................. 19
Non-target fish species ........................................................................... 20
Benthic species ...................................................................................... 21
Catch comparison from sampled hauls ............................................................... 22
Overall categories .................................................................................. 22
Landings (‘lan’), discards of target species (‘cdi’), discards of non-target
fish species (‘fdi’), discards of benthos (‘ben’). .................... 22
Target species ....................................................................................... 24
Plaice
.................................................................................... 24
Sole
.................................................................................... 25
Dab
.................................................................................... 26
Brill
.................................................................................... 27
Turbot
.................................................................................... 28
Whiting
.................................................................................... 29
Cod
.................................................................................... 30
Length dependency of results for major target species.......................................... 33
Plaice
......................................................................................... 33
Sole
......................................................................................... 33
Dab
......................................................................................... 34
Spinal damage of cod ...................................................................................... 34
Spinal damage of whiting ................................................................................. 34
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5.
Discussion ..................................................................................................... 34
6.
Conclusions .................................................................................................... 36
7.
Acknowledgements ......................................................................................... 36
8.
Quality Assurance ........................................................................................... 37
References .............................................................................................................. 37
Justification ............................................................................................................. 38
Appendix A. Cruise reports ........................................................................................ 39
Appendix B. Trawl lists of the three vessels .................................................................. 43
Appendix C. Auction lists of the three vessels ............................................................... 48
Appendix D. Tables of observations on conditions of spine of filleted cod .......................... 50
Appendix E. Digital photographs of filleted cod ............................................................. 54
GO4 Cod (week 42, 2011 after the trials) ........................................................... 54
TX36 Cod
57
TX36 Whiting ................................................................................................. 59
TX68 Cod
62
Appendix F. Raising procedures .................................................................................. 64
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Report number C122b/11
Summary
Comparative fishing trials were conducted in May 2011 (week 19) on commercial beam trawlers fishing
with conventional tickler chain beam trawls (on MFV GO4), pulse wings made by HFK-Engineering of
Baarn, the Netherlands (MFV TX36), and pulse trawls produced by the DELMECO-Group of Goes, the
Netherlands (version used on MFV TX68). The three vessels fished side-by-side as much as possible.
Landings and discards of these vessels were monitored. Special emphasis was given on cod and whiting,
that were dissected to study possible spinal damage. Result for TX36 and TX68 are expressed in terms of
percentages of GO4.
The pulse characteristics were as follows: TX36: voltage 45 V0 to peak, pulse frequency: 45 Hz, pulse
duration 380 µs; electric power on single gear: 7.0 kW; TX68: voltage 50 V0 to peak, pulse frequency: 50 Hz,
pulse duration 220 µs; electric power on single gear: 8.5 kW. The fuel consumption recorded over the
whole week was considerably lower for the pulse trawls, i.e. on TX36 (40%) and on TX68 (54%), than
for the tickler chain beam trawls used on the GO4. The net earnings (taken as gross earnings minus fuel
costs) for the TX36 were almost twice as large at 186%, and for the TX68 also considerably higher at
155%.
The vessels with pulse trawls caught fewer (65-69%) target species, but also less (30-50%) immature
and non-target fish ('discards'), and benthic species (48-73%) than the vessel with tickler chains on
these fishing grounds and in this period. The pulse gears caught fewer (19-42%) kg per hour cod than
the tickler chain beam trawls, but the catches of cod on all three vessels were very small.
For plaice and dab these differences were statistically proven, for brill, turbot and cod this was not the
case. There was no marked difference between both pulse trawl vessels in total landings. The TX68
caught less marketable sole, but not significantly less undersized sole than the GO4. The TX36 caught
less undersized sole, but here the difference in marketable fish was not significant. Catches of brill and
turbot were so small that no statistically substantiated conclusion could be drawn. Only for undersized
turbot the TX36 caught less. For whiting we found a demonstrable reduction in both marketable and
undersized fish in both pulse fishing vessels. The TX36 caught less whiting in number per hour.
The CPUEs found from the auction data and the sampled hauls correlated reasonably well for the most
abundant species, such as plaice and sole. However, for less abundant species the results did not match
very well, and care should be taken to increase the sampling rate in future comparative fishing studies.
Spinal fracture in cod occurred under pulse stimulation but to a limited extent in both marketable and
undersized fish. There is an indication that this happens slightly more on TX68 (11%) than on TX36
(7%). Whiting hardly seems to suffer any damage.
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1.
Introduction
Research into the possible effects of the Verburg-DELMECO pulse trawl on the ecosystem has been carried out since 1998. These effects were studied by looking at catches of target species, by-catches of
undersized fish and benthos, and bottom impact, first with a prototype with 7m beam width, later with a
12 m prototype.
In 2006 and 2009 ICES gave advice on pulse trawling (at the request of the European Commission). In
its advice ICES was on the whole positive about the potential effects of the pulse trawl, but also raised
some additional questions. In the advice of 2006, the following recommendations were given (ICES,
2010):
“Further tank experiments are needed to determine whether injury is being caused to fish escaping from
the pulse trawl gear. The experiments need to be conducted on a range of target and non-target fish
species that are typically encountered by the beam trawl gear and with different length classes. In these
trials it should be ensured that the exposure matches the situation in situ during a passage of the pulse
beam trawl. Fish should be subjected to both external and internal examination after exposure.
If the pulse trawl were to be introduced into the commercial fishery, there would be a need to closely
monitor the fishery with a focus on the technological development and bycatch properties.”
Following the ICES advice of 2006, IMARES conducted tank experiments in 2007-2009 (de Haan et al.,
2008, de Haan et al., 2009; of Marlen et al., 2009; of Marlen et al., 2007), which in 2009 led to further
questions from ICES. The recommendation by ICES goes beyond identifying the current effects of pulse
fishing. In fact, ICES also asked for a method of monitoring and controlling future developments.
It is important to not only look at technical aspects, but also explicitly at policy related issues. Any
decision to remove the current prohibition of using electricity in fishing from the existing regulation is will
only take place only if, there is sufficient confidence within the European member states that removing
the ban will not lead to uncontrolled growth in fishing efficiency.
In the past the research activities dealt with the pulse trawl developed by Verburg Holland Ltd. (further
denoted as Verburg, recently acquired by the DELMECO-group). All results and evaluations were based
on the specifications of the Verburg-DELMECO gear. Meanwhile, the 'sumwing' and later 'pulse wing'
made by HFK Engineering entered the market, and so a new situation has emerged.
2.
Assignment
In view of the advice of ICES and taking into account current developments in pulse trawl gears, the
following objectives were defined:
1.
To monitor catches and by-catches on-board vessels fishing with HFK-pulse wings, with
DELMECO-pulse trawls), and with conventional tickler chain beam trawls, with a particular
emphasis on cod and possible spinal damage due to pulse stimulation.
2.
To bring the research on pulse trawls on an international level by inviting foreign experts to join
the comparative fishing experiments.
This report gives the outcome of the research on these two objectives.
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Report number C122b/11
3.
Materials and Methods
Foreign experts
Three scientists from ILVO, Ostend, Belgium joined on the trials, one on each vessel, all are given in the
list of authors.
Vessels
The trials were carried out on three vessels, MFV TX36 (fishing with HFK pulse wings), MFV TX68 (fishing
with DELMECO pulse trawls), and MFV GO4 (fishing with conventional tickler chain beam trawls), Figure
3-1 and Figure 3-2.
Figure 3-1: TX36 (left), TX68 (middle) en GO4 (right) fishing ‘side-by-side’
The main particulars of these vessels are given below.
Table 3-1: Main particulars of participating vessels
Vessel
TX36
TX68
GO4
Length o.a. (m)
42.35
41.15
40.11
Beam (m)
8.50
8.50
8.50
Depth (m)
5.15
5.30
4.71
Main engine power
1999 hp; 1470 kW
2000 hp; 1471 kW
1995 hp; 1467 kW
Gross Tonnage (GT)
494
438
417
Year of built
2000
1993
1992
Fishing gear used
HFK Pulse wing 12 m
DELMECO pulse trawl
Tickler chain beam
12 m
trawl 12 m
Fishing gears
All cod-ends were made of the same batch of netting with a nominal mesh size of 80 mm to avoid differences due to mesh size. Measurements were done to check mesh sizes. A total of 25 meshes were measured on-board GO4 both on the port and starboard side, and at the beginning and end of the trials. Mesh
sizes were only measured at the beginning of the trials on the TX36. No data was supplied for the TX68,
but measurements were done prior to the trials, and a nominal mesh size of 80 mm reported.
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A T-test was used to see whether the average of both sets of observations differed. This was the case for
GO4 (T-test, p<0.05), but not for the TX36 (Table 3-2).
Table 3-2: Results of mesh size measurements in the cod-ends used onboard GO4 and TX36. P: port, S:
starboard
Ship:
Method:
Gear Type:
# meshes
# meshes
GO4
OMEGA
Beam trawl
25
25
P
S
80.56
81.52
2.81
3.18
80.92
81.96
2.86
2.68
20
20
P
S
79.65
80.75
1.69
1.37
Date:
Mean.
08/05/2011
Stdev.
Mean.
13/05/2011
Stdev.
TX36
OMEGA
Date:
Mean.
Stdev.
08/05/2011
Pulse wing
T-test type
p-value
two-sample,
unequal variance
0.2638
0.1910
two-sample,
unequal variance
0.0301
Figure 3-2: Fishing gears used, left on-board TX36, mid TX68 en right GO4
GO4 fished with two conventional 12 m tickler chain beam trawls, of which technical data are given in
Table 3-3. The gears were fitted with 8 tickler chains and 10 net ticklers.
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Table 3-3: Technical data for GO4
Item
Value
Warp load port side (P, tonne)
9 → P-net harder on-bottom than S-net
Warp load starboard side (S, tonne)
10 → older net
Towing speed (knots)
6 – 6.7
Motor r.p.m.
860
Fuel consumption (ltr)
33000 in 4 days (of 24 h)
Beam trawl shoe weight (kgf)
750 per shoe
Beam length (m)
12
Length tickler chains (m) → 26 mm (n=8)
25.50; 24.00; 22.60; 21.30; 20.10;
19.00; 18.00; 17.00
Length net ticklers (m) → 26 mm (n=2)
3.40; 3.70
Length net ticklers (m) → 22 mm (n=1)
5.20
Length net ticklers (m) → 20 mm (n=2)
6.30; 4.30
Length net ticklers (m) → 18 mm (n=1)
7.30
Length net ticklers (m) → 14 mm (n=4)
8.20; 9.20; 10.20; 11.20
Ground rope length (m)
34
Mesh sizes used

Net (cm)
40; 20; 12 from beam to cod-end

Extension and cod-end (cm
9; 8.1 (cod-end)

Chafing bag (cm)
24

Side panel (cm)
12

Belly (cm)
12
Warp length (m)
4 x water depth
Quotum (tonne)
240 plaice; 150 sole
The pulse wing is a trawl in which the ‘SumWing’ concept is integrated with pulse stimulation, and was
used onboard TX36. A total of 28 pulse modules spaced 41.5 cm apart are placed inside the wing and
connected with parallel electrodes. The dimensions of the wing and electrodes are given in Figure 3-3,
and weights in Table 3-4. The electrode array extends over ~6 m. The nets used on TX36 differ from the
conventional model. The aft part was made of two identical parts next to each other (Figure 3-4).
Table 3-4: Technical data for pulse wing of TX36
Item
Value
Warp load (tonne)
3
Weight in air (kgf)
2800
Weight in water (kgf)
800
Groundrope length (m)
36
Diameter discs on groundrope (mm)
200
Towing speed (knots)
5
Mesh sizes used

Net (cm)
22; 10 from beam to cod-end
In practice warp loads of 4 tonnes are also used while fishing. This requires an alternative setting of the
angle of incidence to avoid the wing lifting the sea bed (Info: Harmen Klein Woolthuis, HFK Engineering,
Baarn, the Netherlands).
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Figure 3-3: Construction drawing of pulse wing and electrodes on TX36
The DELMECO pulse trawl has 25 electrode across its width spaced 42.5 cm apart, and was used onboard
TX68. A square box had been placed behind the beam to carry electronic circuits and a unit on top of the
beam in the centre (Figure 3-5). This configuration was hydro-dynamically non-optimal.
The nets used on TX68 were derived from the conventional beam trawl design. The mesh size in the
square was 20 cm, connected to netting of 10 cm mesh size (Figure 3-6; Table 3-5).
It should be stated that this report relates to the state of technology prior to May 2011 (week 19), and
the technical configuration has been improved since, e.g. for the DELMECO pulse trawls, in which at
present a wing-shaped beam is used, but still with two beam trawl shoes (Personal communication Ko
Zwemer of DELMECO).
Table 3-5: Technical data for pulse wing of TX68
Item
Value
Groundrope length (m)
32
Groundrope weight under water(kgf)
30
Diameter discs on groundrope (mm)
240
Towing speed (knots)
5
Mesh sizes used

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Net (cm)
20; 10 from beam to cod-end
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Figure 3-4: Net drawing TX36, upper: front part, lower: top (left) and bottom (right) panel of the two aft parts
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Figure 3-5: Construction drawing of pulse trawl and beam, electrodes on TX68
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Figure 3-6: Net drawing TX68
Pulse stimulation
Field strength measurements were carried out on-board MFV “Dirkje” TH10 and on MFV “Buis” OD17 in
November 2011 with gears laid on the bottom. TH10 is a euro-cutter, but the electrode length, spacing
and other dimensions were fully comparable to the ones used on TX68. OD17 used the same gear configuration as has been used on TX36 in May 2011 (Table 3-6).
Table 3-6: Overview of main pulse parameters of the two systems (from: De Haan et al., 2011)
Electric
Pulse system
power
TX68
Pulse
Pulse
Voltage
Freq.
duration
(V0 to peak)
(Hz)
(µs)
5.5
50
40
220*
7
45
45
380
single gear
(kW)
DELMECO
Electrode
Electrode
Distance
Conductor
(m)
(nr) (l x d (mm))
25
0.425
6 (180x26)
28
0.415
Nr
2 (125x27) +
HFK TX36
10 (125x33)
*The pulse duration refers to the a single pulse period
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Comparative fishing
The fishing trials were conducted in week 19 (08/05/2011-13/05/2011) with the three vessels fishing
‘side-by-side’ as much as possible given the differences in towing speeds. A total of was 45 hauls were
done on-board the TX36 and the GO4, and 48 on the TX68 (Table 3-7). The positions fished are given in
Figure 3-7.
Figure 3-7: Fished positions (red = GO4; green =TX36; blue = TX68)
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Data collection
Detailed cruise reports are added (See Appendix A). For data collection the so-called ‘discard’-protocol of
IMARES was used, with extra emphasis on cod. This protocol is described in detail in “Handboek discards”
of IMARES (Anonymous, 2010).
Total catch volume was measured using special catch sampling bins constructed on-board, with which the
number of baskets could be counted. Samples were taken of landings and discards for 56-70% of all
hauls (Table 3-7). Fish were measured in cm-below, benthos recorded by species and number, and data
fed in IMARES input program Billie Turf™ with sampling factors related to total catch by weight. Data on
environmental conditions (vessel, trip and haul number, port of call, times of leaving and entering port,
gear used, date-time of shooting, date-time of heaving, haul duration, shooting position, heaving position, distance covered or towing speed, water depth, wind speed and wind direction) and estimated catch
per species were recorded by haul on a ‘trawllist’ in MicroSoft Excel™ for plaice (Pleuronectes platessa
L.), sole (Solea vulgaris L.), dab (Limanda limanda L.), turbot (Psetta maxima L.), brill (Scophthalmus
rhombus L.), cod (Gadus morhua L.), whiting (Merlangius merlangus L.), Norway lobster (Nephrops
Norvegicus L.) and other (See Appendix B).
Landed catches were also recorded on ‘auctionlists’ in Excel in market categories (See Appendix C). By
dividing with total fishing duration CPUE in kg/h was calculated. The following minimum landing sizes
(MLS) were used, based on auction data: plaice 27 cm, sole 24 cm, dab 23 cm, turbot 25 cm, brill 25 cm,
lemon sole 25 cm, flounder 25 cm, whiting 27 cm, cod 35 cm, tub gurnard 28 cm and grey gurnard 28
cm.
All cod that were captured on the TX36 and TX68, were measured and filleted, by which spines were
made visible for inspection and digitally photographed (See Appendix E). The corresponding haul numbers were also recorded for each fish (See Appendix D). On the TX36 this was also done for whiting.
During the trials cod were inspected visually and manually on the GO4, but not internally investigated. At
the time no spinal fractures were seen. Because there were still some doubts whether cod in the tickler
chain beam trawl may get damaged a box of landed cod was purchased from the GO4 in October 2011
(week 42) measured, filleted and photographed (See Appendix E).
Table 3-7: Summary of total number of hauls in which landings (Land) or discards (Disc) were sampled.
week
SHIP
land_hauls
disc_hauls
Total_hauls
Total_h
Land_h
Disc_h
Land_perc
Disc_perc
19
GO4
34
34
45
74
52
52
70.3%
70.3%
19
TX36
33
33
45
80
55
55
68.8%
68.8%
19
TX68
28
33
48
82
46
54
56.1%
65.9%
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Statistical analysis
Data were checked and corrected and then put into IMARES-database FRISBE, after which a SASTM-dataset was made for analysis.
It appeared to be the case that some fish larger than MLS were classified as discards and fish smaller
than MLS as landings. Code was written in SAS to correct these fish and put them in the right category.
SAS-code was also written for making ‘boxplots’ or box-and-whisker diagrams (SAS PROC BOXPLOT),
giving the mean (using symbol +), lower quartile, median, upper quartile, as well as the smallest observation (sample minimum) and the largest observation (sample maximum) for each of the three vessels.
We used a generalized linear model (SAS PROC GLM) of the form:
Dependent variable (log CPUE) = ship (independent variable)
The CPUEs in #/h or kg/h were log-transformed to ensure normality of the residuals. With PROC GLM we
investigated whether the independent variable ship contributed significantly to the variance of the
results, in other words whether CPUE differences were really caused by the vessel (and gear).
In this analysis we looked at catches in overall categories (landings and discards (benthos and fish
(undersized target and non-target species)) as well as catches by species separately: plaice, sole, dab,
brill, turbot, whiting and cod.
The mean CPUE (in #/h or kg/h) over sampled hauls in which catches were found were calculated by
category or by species. PROC GLM also supplies the 95% confidence limits. By comparing these limits for
the three vessels one can deduct whether differences are statistically significant (further denoted as ‘s’)
or non-significant (denoted as ‘ns’). When the confidence limits do not overlap a difference is statistically
significant (s).
We also used SAS-code to raise CPUEs to trip level by using the fraction of total sampled haul duration
over total fishing duration (of all hauls added). Where appropriate calculated weights were corrected with
total weight by species found recorded at the auction. Details of raising procedures are given in Appendix
F.
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Length dependency of results for major target species
Recently software code was developed for analysing catch comparisons to appraise the catch efficiency
(at length) of one gear relative to that of another gear, which deviates from the classical selectivity
experiment where one of the gears is assumed to catch the entire population (Holst and Revill, 2009).
They used ‘Generalised Linear Mixed Models (GLMM)’ and polynomial approximations for the logistic
function describing the probability of retaining a fish at length in what they call the ‘test’ gear, related to
the total catch in the ‘test’ and ‘control’ gear. The binomial probability distribution, which is a function
used for discrete data giving the number of successes in a sequence of n independent yes/no experiments (fish entering a gear compartment or not), each of which yields success with probability p.
In selectivity experiments the selectivity curve can be fitted for each haul, given the data is adequate,
and mean curves can be calculated for a range of hauls. In the case of catch comparisons there is no
data set describing the control values of the entire population, and therefore low-order polynomial
approximations are used. The method gives approximated means and 95% confidence bands at length
for the logit of the expected proportion of the total catch caught in the test cod-end. The line of 0.5
corresponds with equal catches in both gears. When the confidence bands are narrow, the result is more
clearly distinguishable from chance events. Often one sees confidence bands widen when fish are less
abundant, e.g. at higher lengths. The method starts with 3rd order polynomials, and reduces the order
until all terms are significant. Usually a 2nd order fit is sufficient.
We compared hauls for this analysis which are paired in time (having more or less the same start and
end times) and looked at TX36 vs. GO4, TX68 vs. GO4, and TX36 vs. TX68. The GO4 (conventional gear)
is used as control in the first two comparisons with the pulse trawls as test gear, while the TX68 in the
last one, with the TX36 as test gear.
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4.
Results
Overall performance
The TX36 preformed best in terms of Net Revenue, followed by the TX68. The lower fuel consumption for
TX36 was the main reason, as Gross Revenues were about the same for both pulse trawl vessels. Both
pulse trawl vessels caught a much smaller mean number of baskets per sampled haul. In spite of the
higher earnings on GO4, the higher fuel costs of this boat caused a lower economic performance (Table
4-1).
Table 4-1: Summary of overall performance for the three vessels
Mean
Fuel
number of
Fuel
Perc.
baskets
costs
Ship
Gross
Net
Revenue
Revenue
(kg)
(€)
(€)
(%)
Perc.
Landings
(%)
(35 kg)
Perc.
per haul
(x1000
ltr)
(%)
(€; 1 ltr = 0.56€)
GO4
35
100
19600
30
100
6620
29000
9400
100
TX36
14
40
7840
10
32.9
4580
25366
17526
186
TX68
19
54
10640
12
40.1
5078
25192
14552
155
Landings recorded at the auction
Based on auction data and total fishing time the GO4 caught most marketable fish in kg/h, i.e. 90, followed by TX68 (63) then TX36 (58), see Table 4-2. The split in species is also given in this table. Cod on
the two pulse trawl vessels were not actually landed, but their weights calculated by market grade from
the length measurements of the dissected and photographed fish. Most cod was caught by GO4 (1.8
kg/h), followed by TX36 (0.8) and TX68 (0.3).
Table 4-2: Summary of Catches Per Unit of Effort (CPUEs) based on auction data
ship
GO4
TX36
TX68
TX36/GO4
TX68/GO4
TX36/TX68
species
kg/h
kg/h
kg/h
%
%
%
PLE
34.9
24.7
25.2
70.8%
72.1%
98.2%
SOL
17.6
14.8
15.4
84.4%
87.4%
96.6%
DAB
3.4
2.5
4.6
73.9%
135.4%
54.6%
TUR
3.6
3.1
2.8
85.3%
78.4%
108.9%
BLL
2.0
2.1
2.0
103.7%
99.8%
103.9%
COD
1.8
0.8
0.3
42.3%
19.2%
220.8%
WHG
2.7
0.1
1.3
3.2%
47.0%
6.9%
NEP
0.0
0.0
0.0
n/a
n/a
n/a
VAR
24.1
10.4
11.0
43.2%
45.6%
94.6%
Landings (sum)
90.1
58.4
62.5
64.9%
69.4%
93.4%
18 of 67
Report number C122b/11
Landings and discards raised to total trip duration
Target fish species
Landings and discard data for major target species raised to total trip duration are given in Table 4-3.
Expressed in percentage of the total number or weight for plaice and sole we see a small decline for both
pulse trawls.
Table 4-3: Landings and discards of target species cod, dab, plaice, sole and whiting raised to total trip duration
(perc_n and perc_w are percentages in number (n) and weight (w) of discards related to total catch (landings +
discards) for that species)
total
fishing
time
(min)
measured
(kg)
landings
(kg)
landings
(kg/h)
landings
(#/h)
discards
(kg/h)
discards
(#/h)
56.6
1052.0
106.8
ship
species
GO4
Cod
4410
perc_n
perc_w
GO4
Dab
4410
GO4
Plaice
4410
287.0
2565.0
34.9
101.7
1443.9
93
75
GO4
Sole
4410
292.5
1291.0
17.6
72.3
GO4
Whiting
4410
2.8
41.2
36
14
9.9
111.8
TX36
Cod
4775
0.0
0.1
TX36
Dab
4775
16.3
290.2
TX36
Plaice
4775
202.8
1965.0
24.7
71.3
49.6
624.7
90
67
TX36
Sole
4775
188.0
1180.0
14.8
61.4
TX36
Whiting
4775
1.0
10.8
15
6
1.1
14.8
TX68
Cod
4900
0.2
1.0
TX68
Dab
4900
24.7
459.9
TX68
Plaice
4900
112.0
2054.0
25.2
72.3
61.2
TX68
Sole
4900
123.0
1254.0
15.4
56.1
1.7
833.0
92
71
18.7
25
10
0.4
TX36 caught less marketable plaice (s) raised to total trip duration than GO4 (70.8% in kg/h and 70.2%
in #/h), and also discards (46.4% in kg/h and 43.3% in #/h). For TX68 we found: landings (72.1% in
kg/h en 71.1% in #/h) and discards (57.3% in kg/h and 57.7% in #/h), see Table 4-4.
TX36 caught fewer marketable sole raised to total trip duration than GO4 (84.4% in kg/h and 84.9% in
#/h), and also less undersized sole (36.0% in kg/h and 26.2% in #/h). For TX68 these values were:
landings (87.4% in kg/h and 77.5% in #/h) and undersized sole (62.0% in kg/h and 45.4% in #/h), see
Table 4-4.
Table 4-4: Comparison of landings and discards of target species plaice and sole raised to total trip duration
species
comparison
Landings
Landings
Landings
discards
Discards
(kg)
(kg/h)
(#/h)
(kg/h)
(#/h)
Plaice
TX36/GO4
76.6%
70.8%
70.2%
46.4%
43.3%
Sole
TX36/GO4
91.4%
84.4%
84.9%
36.0%
26.2%
Plaice
TX68/GO4
80.1%
72.1%
71.1%
57.3%
57.7%
Sole
TX68/GO4
97.1%
87.4%
77.5%
62.0%
45.4%
Report number C122b/11
19 of 67
Non-target fish species
Table 4-5: CPUE in #/h raised to total trip duration of non-target fish species for the three vessels with the ratio
pulse gear/conventional beam trawl in %
Species
Name (EN)
Pomatoschistus sp.
#/h GO4
#/h TX36
#/h TX68
TX36/GO4
TX68/GO4
1.9
2.56
1.08
137.1%
57.9%
Callionymus lyra
Dragonet
25.2
9.77
50.16
38.8%
199.0%
Hyperoplus lanceolatus
Greater sand-eel
11.1
5.95
3.65
53.5%
32.8%
Clupea harengus
Herring
0.0
0.22
0.00
Agonus cataphractus
Hooknose
3.3
5.22
4.50
158.2%
136.4%
Trachurus trachurus
Horse mackerel
19.9
1.60
2.53
8.0%
12.7%
Echiichthys vipera
Lesser weever
17.8
3.93
21.02
22.1%
118.2%
Cyclopterus lumpus
Lumpsucker
0.3
0.00
0.26
0.0%
78.9%
Callionymus reticulatus
Reticulated dragonet
0.0
6.47
0.00
Arnoglossus laterna
Scaldfish
35.1
27.99
20.54
79.6%
58.4%
Taurulus bubalis
Sea scorpion
1.8
0.00
0.00
0.0%
0.0%
Buglossidium luteum
Solenette
55.5
49.00
39.52
88.2%
71.2%
Sprattus sprattus
Sprat
1.6
0.00
0.00
0.0%
0.0%
Trisopterus luscus
bib
65.0%
82.8%
0.0
0.00
0.37
173.50
112.69
143.63
TX36 caught less in #/h of all species added together than TX68 compared to GO4, but looking at individual species catches of Pomatoschistus and hooknose (Agonus cataphractus L.) were higher. The most
abundant species were solenette (Buglossidium luteum L.), followed by scaldfish (Arnoglossus laterna
L.), dragonet (Callionymus lyra L.), and lesser weever (Echiichthys vipera L.), (Table 4-5).
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Report number C122b/11
Benthic species
Table 4-6: CPUE in #/h raised to total trip duration of non-target benthic species for the three vessels with the
ratio pulse gear/conventional beam trawl in %
Species
Name (EN)
Ammodytes sp.
Anthozoa
Asterias rubens
common star fish
Buccinum undatum
Cancer pagurus
#/h GO4
#/h TX36
#/h TX68
TX36/GO4
TX68/GO4
15.0
9.61
5.28
64.1%
35.2%
3.1
0.87
0.37
27.7%
11.8%
1321.4
683.67
837.32
51.7%
63.4%
3.0
0.00
0.00
0.0%
0.0%
2.3
0.73
0.76
31.6%
33.3%
37.9
58.37
18.38
153.8%
48.4%
5.9
0.00
0.00
0.0%
0.0%
4.7
89.71
287.26
1893.5%
6063.0%
Ensis sp.
4.5
1.49
0.45
32.7%
9.8%
Hyas coarctatus
0.9
0.29
0.00
33.9%
0.0%
Laevicardium crassum
0.0
0.29
0.00
21.9
10.06
12.91
46.0%
59.1%
64.2%
75.2%
375.3%
11.7%
147.4%
Corystes cassivelaunus
Echinidae
Echinocardium cordatum
sea potato
Liocarcinus depurator
Liocarcinus holsatus
1483.7
952.24
1115.83
Liocarcinus marmoreus
swimming crab
0.0
11.98
11.80
Loligo sp.
1.9
7.14
0.22
Loligo subulata
0.0
0.00
0.63
Necora puber
2.0
0.00
2.98
0.0%
1802.3
1538.56
164.99
85.4%
9.2%
208.4
369.46
54.96
177.3%
26.4%
Psammechinus miliaris
0.0
5.37
5.62
Spatangus purpureus
5.6
0.00
0.00
0.0%
0.0%
Spisula sp.
1.5
0.00
0.00
0.0%
0.0%
31.4
14.74
28.09
47.0%
89.5%
0.7
0.00
1.49
0.0%
225.4%
Ophiura ophiura
brittle star
Pagurus bernhardus
hermit crab
Myoxocephalus scorpius
Bull-rout
Mytilus edulis
Common mussel
Crangon crangon
Common shrimp
14.2
29.15
7.07
205.6%
49.9%
4972.35
3783.72
2556.41
76.1%
51.4%
The most abundant benthic species in the catches were brittle star (Ophiura ophiura L.), swimming crab
(Liocarcinus holsatus L.), common star fish (Asterias rubens L.) and hermit crab (Pagurus Bernardus L.).
When adding all catch components TX68 caught less than TX36 compared to GO4. The only remarkable
difference in the pulse trawls was the higher catch of sea potato (Echinocardium cordatum L.), (Table
4-6).
Report number C122b/11
21 of 67
Catch comparison from sampled hauls
Overall categories
Landings (‘lan’), discards of target species (‘cdi’), discards of non-target fish species (‘fdi’), discards of
benthos (‘ben’).
The results given in the BoxPlots are calculated means over the sampled hauls, and not raised to trip
duration.
600
6000
500
5000
n
_ 400
h
l 300
_
h 200
r
n
_ 4000
h
l 3000
_
h 2000
r
100
1000
0
0
GO4
TX36
TX68
GO4
ship
TX36
TX68
ship
Figure 4-1: BoxPlots for left: landings per unit of effort (‘lan’) and right: discards per unit of effort of undersized
target species (‘cdi’) expressed in mean #/h over sampled hauls
125
400
100
w
_
h
l
_
h
r
w 300
_
h
l 200
_
h
r
100
75
50
25
0
0
GO4
TX36
ship
TX68
GO4
TX36
TX68
ship
Figure 4-2: BoxPlots for left: landings per unit of effort (‘lan’) and right: discards per unit of effort of undersized
target species (‘cdi’) expressed in mean kg/h over sampled hauls
The GO4 (273.9 ± 110.0) caught more landings (s) in numbers per hour (#/h) than the TX36 (93.5 ±
54.8) and TX68 (87.8 ± 54.7), with no differences (ns) between the two pulse vessels. Both pulse vessels caught fewer (s) discards of undersized target species (GO4: 2826.0 ± 1112.4; TX36: 959.9 ±
427.4; TX68: 1416.9 ± 447.3, see Figure 4-1 and Table 4-7. In kg/h both pulse trawlers caught less (s)
marketable target species (GO4: 67.4 ± 27.3), (TX36: 22.9 ± 13.0) and (TX68: 20.5 ± 12.6), and fewer
discards (s) of undersized target species (GO4: 188.7 ± 80.4; TX36: 70.2 ± 31.5; TX68: 95.3 ± 31.8),
see Figure 4-2 and Table 4-7.
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Report number C122b/11
1000
15000
12500
800
n
_
h
l
_
h
r
n
_ 10000
h
l 7500
_
h 5000
r
600
400
200
2500
0
0
GO4
TX36
TX68
GO4
ship
TX36
TX68
ship
Figure 4-3: BoxPlots for left: discards of undersized non-target species per unit of effort (‘fdi) and right: catches
of benthos per unit of effort of undersized target species (‘ben’) expressed in mean #/h over sampled hauls
80
w 60
_
h
l 40
_
h
r
20
0
GO4
TX36
TX68
ship
Figure 4-4: BoxPlot for discards of undersized non-target species per unit of effort (‘fdi) expressed in mean kg/h
over sampled hauls
For fish discards of non-target species in #/h we found GO4: 250.1 ± 160.8; TX36: 133.4 ± 85.4; and
TX68: 175.3 ± 83.8. TX68 caught less benthos (s) in #/h (GO4: 5126.4 ± 2506.2; TX36: 3763.1 ±
1688.0; TX68: 2550.2 ± 1881.9, see Figure 4-3 and Table 4-7.
For discards of non-target fish in kg/h we found GO4: 11.7 ± 14.6, TX36: 3.5 ± 3.4) and TX68: 6.6 ±
4.7. TX36 caught significantly less (s) than GO4, see Figure 4-4 and Table 4-7.
Report number C122b/11
23 of 67
Target species
Plaice
Some species appear in almost every sample (e.g. plaice, sole, and dab, while others are less frequent
(e.g. brill, turbot, whiting, cod).
400
3000
n 300
_
h
l 200
_
h
r
100
n
_ 2000
h
l 1500
_
h 1000
r
2500
500
0
0
GO4
TX36
TX68
GO4
ship
TX36
TX68
ship
Figure 4-5: BoxPlots for catch per unit of effort of plaice (mean #/h over sampled hauls, left: landings, right:
discards)
100
250
80
200
w
_
h 150
l
_ 100
h
r
50
w
_
h
l
_
h
r
60
40
20
0
0
GO4
TX36
ship
TX68
GO4
TX36
TX68
ship
Figure 4-6: BoxPlots for catch per unit of effort of plaice (mean kg/h over sampled hauls, left landings, right
discards)
The mean CPUE in #/h over the sampled hauls of marketable plaice was highest for GO4 (129.7 ± 85.6),
and lowest for TX36 (59.3 ± 44.3, s) followed by TX68 (65.0 ± 60.0, s difference with GO4). The highest
CPUE in #/h for discard plaice was found for GO4 (1502.2 ± 707.2), with TX36 as lowest (615.7 ± 311.7,
s difference), followed by TX68 (827.6 ± 340.6, s), see Figure 4-5 and Table 4-8.
The CPUEs for undersized plaice in kg/h were: GO4 (35.9 ± 22.6), TX36 (15.7 ± 13.0) and TX68 (16.3 ±
15.3), clearly lower for both pulse trawl vessels (s). For CPUE of undersized plaice in kg/h we found GO4
(111.1 ± 57.4), TX36 (48.9 ± 25.9, s) en TX68 (60.9 ± 25.9, s) also distinctly lower for the pulse trawls,
see Figure 4-6 and Table 4-8.
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Report number C122b/11
Sole
150
200
125
n 150
_
h
l 100
_
h
r
50
n
_ 100
h
l 75
_
h 50
r
25
0
0
GO4
TX36
TX68
GO4
ship
TX36
TX68
ship
Figure 4-7: BoxPlots for catch per unit of effort of sole (mean #/h over sampled hauls, left: landings, right:
discards)
40
15
w 30
_
h
l 20
_
h
r
10
w
_ 10
h
l
_
h 5
r
0
0
GO4
TX36
TX68
ship
GO4
TX36
TX68
ship
Figure 4-8: BoxPlots for catch per unit of effort of sole (mean kg/h over sampled hauls, left: landings, right:
discards)
The mean CPUE in #/h of marketable sole was highest for GO4 (74.1 ± 27.4), followed by TX36 (52.4 ±
15.7, ns difference with GO4) then by TX68 (41.4 ± 20.4, s difference). The highest CPUE for undersized
sole in #/h was also found for GO4 (45.6 ± 46.4), met de TX36 as lowest (13.2 ± 10.8, s), followed by
TX68 (28.2 ± 17.1, ns), see Figure 4-7 and Table 4-8.
Expressed in kg/h we found for marketable sole: GO4 (18.9 ± 6.6), TX36 (15.0 ± 3.7, ns) en TX68 (10.9
± 5.7, s). For undersized sole in kg/h these were: GO4 (3.1 ± 3.6), TX36 (1.2 ± 0.9, s) en TX68 (2.6 ±
1.5, ns difference), see Figure 4-8 and Table 4-8.
Report number C122b/11
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Dab
200
3000
n 150
_
h
l 100
_
h
r
50
n
_ 2000
h
l 1500
_
h 1000
r
2500
500
0
0
GO4
TX36
TX68
GO4
ship
TX36
TX68
ship
Figure 4-9: BoxPlots for catch per unit of effort of dab (mean #/h over sampled hauls, left: landings, right:
discards)
25
200
20
w
_
h 15
l
_ 10
h
r
5
w 150
_
h
l 100
_
h
r
50
0
0
GO4
TX36
TX68
ship
GO4
TX36
TX68
ship
Figure 4-10: BoxPlots for catch per unit of effort of dab (mean kg/h over sampled hauls, left: landings, right:
discards)
More or less the same results were found for dab. The mean CPUE in #/h for marketable dab was for
GO4 (66.8 ± 40.7), then TX36 (32.4 ± 17.9, s) followed by TX68 (21.9 ± 14.3, s). The CPUE for undersized dab in #/h was for GO4 (1094.6 ± 556.4), with TX36 as lowest (287.7 ± 152.2, s), and TX68 in
between (450.7 ± 227.6, s), see Figure 4-9 and Table 4-8.
CPUEs in kg/h for marketable dab were: GO4 (9.7 ± 5.8), TX36 (4.7 ± 2.8, s) en TX68 (3.1 ± 2.1, s).
For undersized dab in kg/h GO4 (58.9 ± 33.4), TX36 (16.2 ± 8.1, s) en TX68 (24.2 ± 13.2, s), see
Figure 4-10 and Table 4-8.
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Report number C122b/11
Brill
25
n 20
_
h
l 15
_
h
r
10
5
GO4
TX36
TX68
ship
Figure 4-11: BoxPlot for catch per unit of effort of brill (mean #/h over sampled hauls, discards)
5
4
w
_
h 3
l
_ 2
h
r
1
0
GO4
TX36
TX68
ship
Figure 4-12: BoxPlot for catch per unit of effort of brill (mean kg/h over sampled hauls, discards)
We did not find any marketable brill in our samples. Undersized brill in #/h resulted in: GO4 (24.0), with
TX36 coming next (10.6 ± 6.5, ns), and TX68 (9.7 ± 0.5, ns) as lowest, see Figure 4-11 and Table 4-8.
CPUEs of undersized brill in kg/h were: GO4 (4.8), TX36 (1.3 ± 0.8, ns) en TX68 (1.0 ± 0.2, ns), see
Figure 4-12 and Table 4-8. Notable is the low number of observations (hauls) at 6.
Report number C122b/11
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Turbot
7.75
35
30
7.50
n
_
h 7.25
l
_ 7.00
h
r
6.75
n
_
h
l
_
h
r
25
20
15
10
5
6.50
0
TX68
GO4
ship
TX36
TX68
ship
Figure 4-13: BoxPlots for catch per unit of effort of turbot (mean #/h over sampled hauls, left: landings, right:
discards)
2.75
6
2.50
w
_
h 2.25
l
_ 2.00
h
r
1.75
w
_ 4
h
l 3
_
h 2
r
5
1
1.50
0
TX68
ship
GO4
TX36
TX68
ship
Figure 4-14: BoxPlots for dab (mean kg/h over sampled hauls, left: landings, right: discards)
In turbot we found a similar trend as in brill. In #/h the mean CPUE for marketable turbot of TX68 was
6.7, with no turbot found in the samples on the other two vessels. For undersized turbot in mean #/h
GO4 caught 32.0, TX36 (7.7 ± 3.0, s) en TX68 (12.0 ± 0.9, ns), see Figure 4-13 and Table 4-8.
Expressed in kg/h we found the CPUE of undersized turbot for TX68 of 1.6, again for the other two boats,
and for undersized turbot in kg/h GO4 5.8, while TX36 gave (1.5 ± 0.7, s) and TX68 (1.7 ± 0.3, ns), see
Figure 4-14 and Table 4-8. Again a low number of observations with only 5 hauls.
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Report number C122b/11
Whiting
400
125
100
n
_
h
l
_
h
r
n 300
_
h
l 200
_
h
r
100
75
50
25
0
0
GO4
TX36
GO4
TX68
TX36
TX68
ship
ship
Figure 4-15: BoxPlots for catch per unit of effort of whiting (mean #/h over sampled hauls, left: landings, right:
discards)
20
40
w 15
_
h
l 10
_
h
r
5
w 30
_
h
l 20
_
h
r
10
0
0
GO4
TX36
ship
TX68
GO4
TX36
TX68
ship
Figure 4-16: BoxPlots for catch per unit of effort of whiting (mean kg/h over sampled hauls, left landings, right
discards)
For marketable whiting we found in #/h for GO4 (51.1 ± 22.6), with lowest values for TX36 (12.9 ±
10.7, s), then TX68 (22.7 ± 16.5, s). For undersized whiting in #/h this resulted in GO4 (159.9 ± 82.3),
again TX36 being lowest (33.3 ± 27.1, s), followed by TX68 (93.0 ± 105.9, s), see Figure 4-15 and Table
4-8.
In kg/h for marketable whiting these were: GO4 (8.7 ± 4.2), TX36 (2.0 ± 1.6, s) and TX68 (3.6 ± 2.5,
s). Undersized whiting in kg/h resulted in: GO4 (14.1 ± 7.8), TX36 (2.5 ± 2.0, s) en TX68 (6.7 ± 7.8, s),
see Figure 4-16 and Table 4-8.
Report number C122b/11
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Cod
20
30
n 15
_
h
l 10
_
h
r
5
n
_ 20
h
l 15
_
h 10
r
25
5
0
0
GO4
TX36
TX68
TX36
ship
TX68
ship
Figure 4-17: BoxPlots for catch per unit of effort of cod (mean #/h over sampled hauls, left: landings, right:
discards)
30
5
25
4
w
_
h 3
l
_ 2
h
r
1
w
_ 20
h
l 15
_
h 10
r
5
0
0
GO4
TX36
TX68
ship
TX36
TX68
ship
Figure 4-18: BoxPlots for catch per unit of effort of cod (mean kg/h over sampled hauls, left: landings, right:
discards)
The CPUE of marketable cod in #/h was for GO4 (4.7 ± 6.6), with TX36 coming next (1.0 ± 0.5, ns) and
TX68 last (0.8 ± 0.3, ns). In the case of undersized cod in #/h no fish were found for GO4, fewest on
TX36 (0.6 ± 0.0, ns), followed by TX68 (17.5 ± 15.4, ns), see Figure 4-17 and Table 4-8.
Expressed in kg/h we found for marketable cod: GO4 (12.6 ± 13.3), TX36 (2.8 ± 1.9, s) en TX68 (1.8 ±
0.8, s). And for undersized cod in kg/h on GO4 none, on TX36 (0.1 ± 0.1, ns) en TX68 (2.7 ± 2.9, ns),
see Figure 4-18 and Table 4-8.
The number of hauls with cod in the samples was low (2 to 13), and conclusions therefore are backed-up
by statistics only for CPUE in kg/h of marketable cod.
30 of 67
Report number C122b/11
Table 4-7: Mean landings and discards over sampled hauls, (green = favourable, red = unfavourable, boldface is significant (s), statistical tests based on logtransformed data)
Ship
GO4
TX36
TX68
TX36/GO4
TX68/GO4
TX36/TX68
GLM_output
Diff
TX36
vs. GO4
Diff
TX68
vs. GO4
Diff
TX36
vs.
TX68
Variable
species
cat
n
Mean
Stdev
n
Mean
Stdev
n
Mean
Stdev
%
%
%
n_hl_hr
lan
lan
33
273.9
110.0
39
93.5
54.8
32
87.8
54.7
34.1%
32.0%
106.6%
s
s
ns
33
67.4
27.3
39
22.9
13.0
32
20.5
12.6
34.0%
30.4%
111.8%
s
s
ns
33
2826.0
1112.4
33
959.9
427.4
33
1416.9
447.3
34.0%
50.1%
67.7%
s
s
s
33
188.7
80.4
33
70.2
31.5
33
95.3
31.8
37.2%
50.5%
73.6%
s
s
s
30
250.1
160.8
33
133.4
85.4
33
175.3
83.8
53.3%
70.1%
76.1%
s
ns
ns
30
11.7
14.6
33
3.5
3.4
33
6.6
4.7
29.9%
56.5%
53.0%
s
ns
s
33
5126.4
2506.2
33
3763.1
1688.0
33
2550.2
1881.9
73.4%
49.7%
147.6%
ns
s
ns
w_hl_hr
n_hl_hr
cdi
dis
w_hl_hr
n_hl_hr
fdi
dis
w_hl_hr
n_hl_hr
31 of 67
ben
dis
Report number C122b/11
Table 4-8: Summary of mean CPUE over sampled hauls expressed in #/h and kg/h for landings (‘lan’) en discards (‘dis’) of plaice (PLE), sole (SOL), dab (DAB),
brill (BLL), turbot (TUR), whiting (WHG) and cod (COD) for the three vessels with the result of the test in significance using the generalized linear model (GLM)
(green = favourable, red = unfavourable, boldface is significant (s), statistical tests based on log-transformed data)
Ship
GO4
TX36
TX68
TX36/GO4
TX68/GO4
TX36/TX68
Diff
TX36
vs. GO4
GLM_output
Diff
Diff
TX68 vs.
TX36 vs.
GO4
TX68
Variable
species
cat
n
Mean
Stdev
n
Mean
Stdev
n
Mean
Stdev
%
%
%
n_hl_hr
PLE
lan
33
129.7
85.6
27
59.3
44.3
20
65.0
60.0
45.7%
50.1%
91.1%
s
s
ns
33
35.9
22.6
27
15.7
13.0
20
16.3
15.3
43.7%
45.4%
96.3%
s
s
ns
33
1502.2
707.2
33
615.7
311.7
33
827.6
340.6
41.0%
55.1%
74.4%
s
s
ns
33
111.1
57.4
33
48.9
25.9
33
60.9
25.9
44.0%
54.8%
80.4%
s
s
ns
33
74.1
27.4
18
52.4
15.7
18
41.4
20.4
70.7%
55.9%
126.5%
ns
s
ns
33
18.9
6.6
18
15.0
3.7
18
10.9
5.7
79.4%
57.8%
137.2%
ns
s
ns
31
45.6
46.4
27
13.2
10.8
22
28.2
17.1
29.0%
61.9%
46.8%
s
ns
s
31
3.1
3.6
27
1.2
0.9
22
2.6
1.5
39.8%
84.5%
47.1%
s
ns
s
23
66.8
40.7
29
32.4
17.9
25
21.9
14.3
48.5%
32.8%
147.8%
s
s
ns
23
9.7
5.8
29
4.7
2.8
25
3.1
2.1
49.2%
32.2%
152.6%
s
s
ns
33
1094.6
556.4
33
287.7
152.2
33
450.7
227.6
26.3%
41.2%
63.8%
s
s
s
33
58.9
33.4
33
16.2
8.1
33
24.1
13.2
27.5%
40.9%
67.1%
s
s
s
1
24.0
.
6
10.6
6.5
2
9.7
0.5
44.4%
40.5%
109.6%
ns
ns
ns
1
4.8
.
6
1.3
0.8
2
1.0
0.2
27.9%
20.5%
136.2%
ns
ns
ns
1
32.0
.
5
7.7
3.0
2
12.0
0.9
24.2%
37.6%
64.3%
s
ns
ns
1
5.8
.
5
1.5
0.7
2
1.7
0.3
26.0%
30.1%
86.5%
s
ns
ns
w_hl_hr
n_hl_hr
PLE
dis
w_hl_hr
n_hl_hr
SOL
lan
w_hl_hr
n_hl_hr
SOL
dis
w_hl_hr
n_hl_hr
DAB
lan
w_hl_hr
n_hl_hr
DAB
dis
w_hl_hr
n_hl_hr
BLL
dis
w_hl_hr
n_hl_hr
TUR
dis
w_hl_hr
n_hl_hr
WHG
lan
w_hl_hr
n_hl_hr
WHG
dis
w_hl_hr
n_hl_hr
COD
lan
w_hl_hr
n_hl_hr
w_hl_hr
32 of 67
COD
dis
14
51.1
22.6
8
12.9
10.7
7
22.7
16.5
25.2%
44.4%
56.7%
s
s
ns
14
8.7
4.2
8
2.0
1.6
7
3.6
2.5
23.2%
41.4%
56.0%
s
s
ns
24
159.9
82.3
15
33.3
27.1
28
93.0
105.9
20.8%
58.1%
35.8%
s
s
s
24
14.1
7.8
15
2.5
2.0
28
6.7
7.8
18.0%
47.6%
37.9%
s
s
ns
5
4.7
6.6
13
1.0
0.5
10
0.8
0.3
21.7%
17.6%
123.5%
ns
ns
ns
5
12.6
13.3
13
2.8
1.9
10
1.8
0.8
21.9%
14.4%
152.1%
s
s
ns
0
n/a
n/a
4
0.6
0.0
2
17.5
15.4
3.7%
ns
ns
ns
0
n/a
n/a
4
0.1
0.1
2
2.7
2.9
4.6%
ns
ns
ns
Report number C122b/11
Length dependency of results for major target species
Plaice
TX36 vs. GO4
TX68 vs. GO4
TX36 vs. TX68
Figure 4-19: Proportion of fish retained in the test net (=test/(test+control) vs. length for plaice (value 0.5
means both gears catch equal numbers, the solid line gives the mean, and the grey band gives the 95%
confidence limit)
TX36 caught fewer plaice over the entire length range than GO4. The difference is lowest around 20 cm,
and especially lower numbers of larger plaice were caught. This is also the case for the TX68, but here
the catch of small fish is equal. When comparing both pulse trawlers TX68 seems to catch more large
plaice, but given the wide confidence bands, this result is uncertain (Figure 4-19).
Sole
TX36 vs. GO4
TX68 vs. GO4
TX36 vs. TX68
Figure 4-20: Proportion of fish retained in the test net (=test/(test+control) vs. length for sole (value 0.5
means both gears catch equal numbers, the solid line gives the mean, and the grey band gives the 95%
confidence limit)
TX36 caught fewer small sole than GO4, while for TX68 there is much uncertainty both for small and
large fish. TX36 appears to catch fewer small and more large sole, but again the conclusion is debatable,
die to the wide confidence bands (Figure 4-20).
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Report number C122b/11
Dab
TX36 vs. GO4
TX68 vs. GO4
TX36 vs. TX68
Figure 4-21: Proportion of fish retained in the test net (=test/(test+control) vs. length for dab (value 0.5
means both gears catch equal numbers, the solid line gives the mean, and the grey band gives the 95%
confidence limit)
The dab results are similar in trend as the sole results, with higher uncertainty (Figure 4-21).
Spinal damage of cod
On GO4 48 cod were filleted and photographed, with only one fish showing a haemorrhage near the
spine in the tail section, but no fracture was seen (Appendix D: Table 8-1; Appendix E: Figure 8-1).
A total of 27 fish were studied on TX36. In 2 individuals spinal fracture was seen, which means 7.4%. For
TX68 these were respectively 18 fish with 2 fractures, thus 11.1% (Appendix D: Table 8-2 and Table
8-3; Appendix E: Figure 8-2 and Figure 8-4). It was notable that spinal fractures appeared both in juvenile and in marketable fish.
The digital pictures show frequent haemorrhages in cod for the pulse trawls and occasionally a fracture of
the spine. This was not the case for the GO4 where cod where photographed later in week 42.
Spinal damage of whiting
On TX36 and TX68 whiting was studied too. Of a total of 47 individuals only one fish on TX36 showed
spinal fracture, a percentage of 2.1%. This injury may have been caused by the electrical stimulus or by
mechanical forces during haul-back and discharge on deck. This fish was 32 cm long while longer fish did
not show any damage (Appendix D: Table 8-4). The filleted fish did hardly show any haemorrhages
(Appendix E: Figure 8-3). On TX68 a total of 10 individuals were taken from the catch and filleted, but
not photographed. These fish showed no fractures or other damages (See Appendix A for TX68).
5.
Discussion
As mentioned earlier in quite a number of hauls undersized fish was scored as landings (cat = ‘l’) and
marketable fish as discards (cat = ‘d’). This can be a result of sorting errors by the crew. As we are
interested in the differences between gear types (pulse vs. conventional) we corrected these scores in
the analysis.
More hauls were sampled on GO4 than on both pulse trawl vessels and also more frequently both plaice
and sole from the same haul. The mean CPUE (kg/h) calculated from sampled hauls deviated for various
species considerably from the CPUEs raised to total trip duration, especially for low number of observations (hauls) in which these species were found. This means that the sampling procedure did not produce
34 of 67
Report number C122b/11
reliable results in all cases. The length-dependent analyses also showed that confidence bands were
often wide indicating that the number of fish measured was low. This means that the results should be
interpreted more in terms of giving a trend than producing absolute comparative data. In future catch
comparisons one should ensure that more fish are sampled and measured to enhance statistical validity.
When comparing the capture efficiency of fishing gears one should accurately document technical and
constructional details. Differences in catch are caused by many factors. Apart from the mesh size in the
cod-ends, the ground rope construction and the netting used play an important role as well. The nets
deployed on TX36 were very different than the usual beam trawl nets with the square front and double
aft parts. We did not investigate these differences in great detail and the questions remains whether the
results may have been affected by the gear differences other than the differences in stimulation. We
cancelled any adverse effect from differences in mesh size by making all cod-ends from the same bale of
netting. This does not exclude any other effects in gear differences completely, but as mesh size is one
of the most determining variables other effects would have likely been small.
When measuring and comparing fish from several gears often numbers at length are found in one of
them, but not in one of the others. Some researchers suggest to set these missing fish at zero catch.
There may be a suit of reasons for fish not appearing in a sample: they may not have been on the
grounds at all in range of a particular net to be caught, as fish distribution is often patchy, they may
have been on the grounds, but out of reach of the net, they may have escaped from the gear, or they
may have missed to be taken in a sample. Diurnal differences in behaviour may cause fish to stay out of
reach, e.g. cod and whiting are usually caught mostly during the night. This problem turned out to be
largest for less abundant species such as: brill, turbot, whiting and cod. We often found low numbers of
hauls for these species in our data. We chose here to not set missing values at zero, and use the data as
they emerged to avoid creating a dataset suggesting outcomes that were not really existing. This does
mean, however, that our conclusions are most valid for the most abundant species such as plaice, sole
and dab, and more uncertain for the other species brill, turbot, whiting, and cod.
When we compared the results with trials conducted in 2006 in which five trips of MFV UK153, fishing
with pulse trawls with five trips with conventional beam trawls (van Marlen et al., 2006), we found, that
the total landings in kg/h, based on the auction data, were in the same order of magnitude for the pulse
trawl vessels in our present experiment. In 2006 we found in total landings for the pulse trawl vessel
some 68% (ranging from 60-70%, with one outlier of 95%), whilst here the results were: 58% for the
TX36 and 63% for the TX68. The catch efficiencies for sole and plaice seemed to have been raised somewhat. Now we found for sole some 84% for the TX36 and 87% for the TX68, then the CPUEs varied
between 66-93% (78% for all trips taken together). For plaice these values were: 71% for the TX36 and
72% for the TX68 %, compared to 53-90% (65% for all trips taken together) in 2006. In our recent
experiments we also did see a significant reduction in the CPUE of undersized sole in comparison with
GO4, based on sampled hauls, for TX36, but not for TX68, whilst the CPUEs for undersized plaice were
now significantly lower for both pulse trawl vessels and this was not the case in 2006.
The CPUEs of benthos (in #/h) were 73% (TX36, ns) and 50% (TX68, s) for the sampled hauls, compared to that of the GO4. The catch comparison of pulse and conventional beam trawls onboard FRV “Tridens” resulted in 75% (in kg/h) for the pulse trawl (van Marlen et al., 2005). In 2006 three benthic species were analysed in detail: sandstar (Astropecten irregularis L.), common starfish (Asterias rubens L.),
and swimming crab (Liocarcinus holsatus L.), which gave catch rates of respectively: 24%, 75% and
53% (in #/h) for the pulse trawl (van Marlen et al., 2006). Now we found for these species: sandstar:
no reported catches, starfish: 52% (TX36) en 63% (TX68), and swimming crab: 64% (TX36) en 75%
(TX68). The catches of starfish seemed somewhat declined, and those of swimming crab increased, but
this conclusion could not be back-up with a statistical test with only one trip in the present dataset.
Report number C122b/11
35 of 67
Pulse trawls are continuously improved, e.g. the DELMECO-group offer a wing-shaped beam instead of
the usual cylindrical in their new versions, but with two trawl shoes per side contrary to the pulse wing.
This means that our conclusions should be restricted to the technical state of the gears as they were
tested in May 2011. On the other hand, when pulse stimulation remains unchanged we may not expect
great differences with the results produced here.
The ICES advice calls for ensuring unlimited growth in capture efficiency of pulse trawls and a proper
control and enforcement regime while enhancing sustainable development in fisheries. In the Netherlands a special task group on control and enforcement issue was established, with representatives of the
Dutch fishing industry, pulse trawl producers, the Directorate of fisheries of the Dutch Ministry of Economic Affairs, Agriculture and Innovation (EL&I), researchers of IMARES and the General Inspection Service
(AID) to address these issues. This group is currently working out additional technical requirements and
requirements on electrical power, voltage used and possibly other important electro-technical variables,
and explores the idea of certification of pulse trawls. The results of this study will be used in the discussions of this group. In addition the wish was expressed for further monitoring of catches, by-catches and
pulse system variables onboard commercial pulse trawl vessels.
6.
Conclusions
In Net Revenue the pulse trawl vessels (TX36 and TX68) fishing with pulse trawls in the version of May
2011 were much more efficient (55-84% higher) than the vessel with conventional beam trawls (GO4),
mainly due to their lower fuel consumption (46-60% lower).
The vessels fishing with pulse trawls caught fewer of the main target species (65-69%), but also less fish
discards (30-50%) and fewer benthic species (48-73%) than the vessel fishing with conventional beam
trawls in this period and on these fishing grounds. Cod catches were very low and smaller catches (1942%) than for the conventional beam trawl could only be proven for marketable sizes in kg/h in both
pulse trawls.
For plaice and dab the differences were statistically significant, but not for brill, turbot, and cod. Both
pulse trawl vessels did not show any significant differences in main target species when compared with
each other. TX68 caught clearly less marketable sole, but not fewer undersized fish than GO4. TX36 did
catch fewer discard sole than GO4, but this was not the case for marketable sizes. TX36 did catch fewer
juvenile sole and dab than TX68. Catches of brill and turbot were so small that statistical evidence of
differences was hardly found. The only significant difference was for small turbot on TX36. Both pulse
trawl vessels caught clearly less undersized and marketable whiting than GO4.
Spinal fractures in cod did occur in the catches of the pulse trawl vessels in both undersized and
marketable fish, but the rate was low at 7-11%. There were hardly any spinal fractures in whiting.
There was a reasonable correlation between CPUEs found from the auction data and the sampled hauls
for the most abundant species, such as plaice and sole. For less abundant species the results do not
match very well, and care should be taken to increase the sampling rate in future comparative fishing
studies.
7. Acknowledgements
The authors are indebted to the Dutch Ministry of Economic Affairs, Agriculture and Innovation (EL&I) for
financially supporting this study, and to the skippers and crew of MFV “Jan van Toon” TX36, MFV “Vertrouwen” TX68, MFV “George Johannes Klazina“ GO4, MFV “Dirkje” TH10 and MFV “Buis” OD17 for their
fine cooperation. In addition we wish to thank F.J. Quirijns of IMARES for constructional criticism.
36 of 67
Report number C122b/11
8.
Quality Assurance
IMARES utilises an ISO 9001:2008 certified quality management system (certificate number: 578462009-AQ-NLD-RvA). This certificate is valid until 15 December 2012. The organisation has been certified
since 27 February 2001. The certification was issued by DNV Certification B.V. Furthermore, the chemical
laboratory of the Environmental Division has NEN-AND-ISO/IEC 17025:2005 accreditation for test
laboratories with number L097. This accreditation is valid until 27 March 2013 and was first issued on 27
March 1997. Accreditation was granted by the Council for Accreditation.
References
Anonymous, 2010. Handboek discards. Versie: 2010. IMARES, IJmuiden, p. 16.
De Haan, D., Fosseidengen, J.E., Fjelldal, P.G., Burggraaf, D., 2011. The effect of electric pulse stimulation to
juvenile cod and cod of commercial landing size. IMARES Report C141/11. p. 45.
De Haan, D., van Marlen, B., Kristiansen, T.S., Fosseidengen, J.E., 2008. The effect of pulse stimulation on
biota - Research in relation to ICES advice - Progress report on the effects to cod. IMARES Report C98/08, p.
22.
De Haan, D., van Marlen, B., Velzenboer, I., van der Heul, J., van de Vis, J.W., 2009. The effects of pulse
stimulation on biota – Research in relation to ICES advice – Effects on dogfish. IMARES Report C105/09, p.
32.
ICES, 2010. Report of the Workshop to Assess the Ecosystem Effects of Electric Pulse Trawls (WKPULSE) - 2426 February 2010, IJmuiden, the Netherlands, p. 36.
ICES, 2011. Report of the Study Group on Electrical Trawling (SGELECTRA). ICES CM 2011/SSGESST:09. p. 93.
Van Marlen, B., de Haan, D., van Gool, A., Burggraaf, D., 2009. The effect of pulse stimulation on marine biota
– Research in relation to ICES advice – Progress report on the effects on benthic invertebrates. IMARES
Report C103/09, p. 49.
Van Marlen, B., Grift, R., van Keeken, O., Ybema, M.S., van Hal, R., 2006. Performance of pulse trawling
compared to conventional beam trawling. RIVO Report C014/06, p. 60.
Van Marlen, B., van de Vis, J.W., de Haan, D., Burggraaf, D., van der Heul, J., Terlouw, A., 2007. The effect of
pulse stimulation on biota – Research in relation to ICES advice – Progress report with preliminary results.
IMARES Report C098/07, p. 24.
Van Marlen, B., Ybema, M.S., Kraayenoord, A., de Vries, M., Rink, G., 2005. Catch comparison of a 12 m pulse
beam trawl with a conventional tickler chain beam trawl. RIVO Report C043b/05, p. 31.
Report number C122b/11
37 of 67
Justification
Rapport C122b/11
Project Number:
430.1301.401
The scientific quality of this report has been peer reviewed by the a colleague scientist and the head of
the department of IMARES.
Approved:
F.J. Quirijns (M.Sc.)
Researcher
Signature:
Date:
22/11/2011
Approved:
T.P. Bult (Ph.D.)
Head Fisheries Department
Signature:
Date:
38 of 67
22/11/2011
Report number C122b/11
Appendix A. Cruise reports
Cruise report TX36
Ship (incl. address)
TX-36 “Jan van Toon”
Vis Vis Ltd.
Wulkpad 2
1794-BK Oosterend, Netherlands
Tel.: +31 222-318651
Year, month, week
2011, May, week 19
Trip number
Scientists
Evert van Barneveld (IMARES)
Eddy Buyvoets (ILVO)
Port of departure, date, time
Oudeschild
8-5-2011
22:00 h
Port of arrival, date, time
IJmuiden
13-5-2011
05:00 h
Gear, mesh size, tickler
Pulse Wing HFK, width 12 m
chains
8 cm mesh in cod-end
Totale catch by species
See auction list
Number of hauls
45
Number of hauls sampled
33 hauls discards sampled
(discards, landings)
33 hauls landings sampled
Weather
Monday to Wednesday very fine weather (wind B 2)
Thursday more wind (B 4)
Comments
One time during the week (during haul 33 after which this haul was
restarted) there was a malfunctioning of the pulse wing with
replacement of a pulse module.
Report number C122b/11
39 of 67
Cruise report TX68
Ship (incl. address)
TX68 “Vertrouwen”
Cor Daalder
email: cordaalder@gmail.com
Cor Bremerstraat 4
Tel: +31 6 1338 6264
1794 AX Oosterend Texel, Netherlands
Year, month, week
2011, May, week 19
Trip number
Scientists
J.A.M. Wiegerinck (IMARES)
Christian van den Berghe (ILVO)
Port of departure, date, time
Oudeschild, Sunday 8 May 2011 at 22.30 h
Port of arrival, date, time
Den Helder, Friday 13 May 2011 at 05.00 h
Gear, mesh size, tickler
Pulse trawl (Delmeco), width 12 m, mesh size 80 mm, no tickler chains
chains
Electrode length (from wing to groundrope): 6 m.
Main engine power 1488 hp (on propeller 1250-1300 hp)
Electrical power: 6 kW
1st mesh size measurement was done on previous Friday in the net loft
(80 mm)
2nd mesh size measurement was done after last haul trek (10 readings
with Omega-meter on each side) resulting in the following averages:
Port side: 83.6 mm
Starboard side: 83.9 mm
Totale catch by species
See auction list
Number of hauls
48
Number of hauls sampled
33
(discards, landings)
Weather
Fine weather, calm see
Comments
Big cod, larger than 50 cm showed little damage. Some haemorrhages
and a few broken spines (see tables on cod observations and photos).
Whiting (some 10 filleted) showed no damage (no photos were taken).
40 of 67
Report number C122b/11
Cruise report GO4
Ship (incl. address)
GO4 “George Johannes Klazina”
't Mannetje & Zn
Bernardstraat 33
3248 AC Melissant, Netherlands
Year, month, week
2011, May, week 19
Trip number
Scientists
E. van Os-Koomen (IMARES)
K. Vanhalst (ILVO)
Port of departure, date, time
Scheveningen, 09-05-2011 at 01.30 h
Port of arrival, date, time
Scheveningen, 13-05-2011 at 01.00 h
Gear, mesh size, tickler
Conventional beam trawl
chains
80 mm mesh in cod-end
12 tickler chains
Totale catch by species
Sole - 1291 kg
Plaice - 2565 kg
Turbot - 263 kg
Brill - 147 kg
Seabass - 94 kg
Cod - 134 kg
Tub gurnard - 1322 kg
Horse mackerel - 95 kg
Red Mullet - 75 kg
Dab - 250 kg
Whiting - 201 kg
Flounder - 120 kg
Number of hauls
45
Number of hauls sampled
33
(discards, landings)
Weather
Fine
Comments
None
Report number C122b/11
41 of 67
Appendix B. Trawl lists of the three vessels
ship
gear
meshsize
haul
year
month
week
day
tset
thaul
duration
poslat
poslon
depth
winddir
windforc
GO4
BT12
80
1
2011
5
19
9
03:15
05:15
120
52.11
3.56
23
135
2
GO4
BT12
80
2
2011
5
19
9
05:40
07:40
120
52.19
3.38
25
180
2
GO4
BT12
80
3
2011
5
19
9
08:15
09:45
90
52.32
3.4
29
180
2
GO4
BT12
80
4
2011
5
19
9
10:00
11:30
90
52.3
3.38
30
180
2
GO4
BT12
80
5
2011
5
19
9
11:45
13:15
90
52.27
3.36
27
180
2
GO4
BT12
80
6
2011
5
19
9
13:45
15:15
90
52.21
3.36
27
180
2
GO4
BT12
80
7
2011
5
19
9
15:30
17:00
90
52.19
3.23
28
180
2
GO4
BT12
80
8
2011
5
19
9
17:20
18:50
90
52.15
3.05
36
180
2
GO4
BT12
80
9
2011
5
19
9
19:10
20:40
90
52.06
2.59
36
180
2
GO4
BT12
80
10
2011
5
19
9
21:00
22:30
90
52.04
2.57
36
180
2
GO4
BT12
80
11
2011
5
19
9
23:15
00:45
90
52
3.06
36
180
2
GO4
BT12
80
12
2011
5
19
10
01:00
03:00
120
52
3.05
34
180
2
GO4
BT12
80
13
2011
5
19
10
03:15
05:15
120
52
3.03
32
180
2
GO4
BT12
80
14
2011
5
19
10
05:30
07:30
120
51.58
3.03
32
180
2
GO4
BT12
80
15
2011
5
19
10
08:00
09:30
90
51.58
3.03
32
180
2
GO4
BT12
80
16
2011
5
19
10
09:50
11:20
90
52.01
3.05
32
180
2
GO4
BT12
80
17
2011
5
19
10
12:00
13:30
90
52.13
3.13
32
180
2
GO4
BT12
80
18
2011
5
19
10
13:50
15:20
90
52.18
3.13
32
180
2
GO4
BT12
80
19
2011
5
19
10
14:45
16:15
90
52.16
3.34
25
180
2
GO4
BT12
80
20
2011
5
19
10
17:35
19:05
90
52.17
3.43
24
180
2
GO4
BT12
80
21
2011
5
19
10
19:20
20:50
90
52.27
3.49
24
180
2
GO4
BT12
80
22
2011
5
19
10
21:10
22:40
90
52.29
3.5
24
180
2
GO4
BT12
80
23
2011
5
19
10
23:30
01:30
120
52.27
3.5
24
180
2
GO4
BT12
80
24
2011
5
19
11
01:45
03:45
120
52.24
3.44
24
180
2
GO4
BT12
80
25
2011
5
19
11
04:00
06:00
120
52.24
3.42
24
180
2
GO4
BT12
80
26
2011
5
19
11
06:20
08:20
120
52.23
3.43
24
180
2
GO4
BT12
80
27
2011
5
19
11
08:45
10:15
90
52.22
3.44
24
180
2
GO4
BT12
80
28
2011
5
19
11
10:30
12:00
90
52.29
3.51
24
180
2
GO4
BT12
80
29
2011
5
19
11
12:25
13:55
90
52.39
3.59
24
180
2
GO4
BT12
80
30
2011
5
19
11
14:15
15:45
90
52.39
3.59
24
180
2
GO4
BT12
80
31
2011
5
19
11
15:45
17:15
90
52.49
3.57
24
180
2
43 of 67
Report number C122b/11
ship
gear
meshsize
haul
year
month
week
day
tset
thaul
duration
poslat
poslon
depth
winddir
windforc
GO4
BT12
80
32
2011
5
19
11
18:05
19:35
90
52.5
4.08
21
225
2
GO4
BT12
80
33
2011
5
19
11
19:50
21:20
90
52.45
4.03
21
225
2
GO4
BT12
80
34
2011
5
19
11
22:00
23:30
90
52.33
4.1
21
225
2
GO4
BT12
80
35
2011
5
19
12
00:00
02:00
120
52.34
4.1
21
225
2
GO4
BT12
80
36
2011
5
19
12
02:30
04:30
120
52.34
4.07
20
225
2
GO4
BT12
80
37
2011
5
19
12
04:50
06:50
120
52.23
3.59
22
225
2
GO4
BT12
80
38
2011
5
19
12
07:10
08:40
90
52.27
3.58
22
225
2
GO4
BT12
80
39
2011
5
19
12
09:00
10:30
90
52.21
3.56
21
225
2
GO4
BT12
80
40
2011
5
19
12
11:00
12:30
90
52.21
4.02
21
315
2
GO4
BT12
80
41
2011
5
19
12
12:45
14:15
90
52.2
4.03
20
315
2
GO4
BT12
80
42
2011
5
19
12
14:40
16:10
90
52.22
3.59
21
315
3
GO4
BT12
80
43
2011
5
19
12
16:30
18:00
90
52.2
4.02
21
270
4
GO4
BT12
80
44
2011
5
19
12
18:15
19:45
90
52.22
4.01
21
270
4
GO4
BT12
80
45
2011
5
19
12
20:00
21:30
90
52.23
4.01
21
270
4
TX36
BT12e1
80
1
2011
5
19
9
01:15
03:40
145
52.52
4.13
24
135
2
TX36
BT12e1
80
2
2011
5
19
9
03:50
06:00
130
52.45
3.48
22
180
2
TX36
BT12e1
80
3
2011
5
19
9
06:20
07:55
95
52.37
3.45
25
180
2
TX36
BT12e1
80
4
2011
5
19
9
08:00
09:50
110
52.31
3.34
24
180
2
TX36
BT12e1
80
5
2011
5
19
9
10:00
11:30
90
52.32
3.36
27
180
2
TX36
BT12e1
80
6
2011
5
19
9
11:45
13:15
90
52.3
3.38
24
180
2
TX36
BT12e1
80
7
2011
5
19
9
13:30
15:00
90
52.22
3.4
25
180
2
TX36
BT12e1
80
8
2011
5
19
9
15:10
16:50
100
52.21
3.27
30
180
2
TX36
BT12e1
80
9
2011
5
19
9
17:00
18:25
85
52.2
3.14
32
180
2
TX36
BT12e1
80
10
2011
5
19
9
18:45
20:30
105
52.14
3.05
36
180
2
TX36
BT12e1
80
11
2011
5
19
9
20:40
22:10
90
52.04
2.56
38
180
2
TX36
BT12e1
80
12
2011
5
19
9
22:25
23:55
90
52
3.08
25
180
2
TX36
BT12e1
80
13
2011
5
19
10
00:10
02:05
115
52.05
2.56
24
180
2
TX36
BT12e1
80
14
2011
5
19
10
02:15
04:05
110
51.59
3.05
26
180
2
TX36
BT12e1
80
15
2011
5
19
10
04:15
06:10
115
51.57
3.05
25
180
2
TX36
BT12e1
80
16
2011
5
19
10
06:20
08:10
110
51.55
3.03
26
180
2
TX36
BT12e1
80
17
2011
5
19
10
08:20
09:45
85
51.55
3.03
28
180
2
TX36
BT12e1
80
18
2011
5
19
10
10:00
11:35
95
52.03
3.06
30
180
2
TX36
BT12e1
80
19
2011
5
19
10
11:45
13:25
100
52.11
3.1
33
180
2
TX36
BT12e1
80
20
2011
5
19
10
13:40
15:20
100
52.17
3.19
24
180
2
44 of 67
Report number C122b/11
ship
gear
meshsize
haul
year
month
week
day
tset
thaul
duration
poslat
poslon
depth
winddir
windforc
TX36
BT12e1
80
21
2011
5
19
10
15:30
17:05
95
52.17
3.44
21
180
2
TX36
BT12e1
80
22
2011
5
19
10
17:25
19:10
105
52.17
3.44
21
180
2
TX36
BT12e1
80
23
2011
5
19
10
19:20
21:05
105
52.21
3.5
23
180
2
TX36
BT12e1
80
24
2011
5
19
10
21:15
23:10
115
52.29
3.54
22
180
2
TX36
BT12e1
80
25
2011
5
19
10
23:20
01:25
125
52.27
3.49
23
180
2
TX36
BT12e1
80
26
2011
5
19
11
01:40
03:35
115
52.23
3.5
23
180
2
TX36
BT12e1
80
27
2011
5
19
11
03:45
05:50
125
52.25
3.48
23
180
2
TX36
BT12e1
80
28
2011
5
19
11
06:20
08:05
105
52.24
3.43
24
180
2
TX36
BT12e1
80
29
2011
5
19
11
08:20
10:05
105
52.19
3.47
24
180
2
TX36
BT12e1
80
30
2011
5
19
11
10:20
12:10
110
52.28
3.48
23
180
2
TX36
BT12e1
80
31
2011
5
19
11
12:35
14:10
95
52.37
3.58
22
180
2
TX36
BT12e1
80
32
2011
5
19
11
14:20
16:00
100
52.45
4.04
23
225
2
TX36
BT12e1
80
33
2011
5
19
11
17:50
19:50
120
52.53
4.04
22
225
2
TX36
BT12e1
80
34
2011
5
19
11
20:05
21:45
100
52.51
4.09
22
225
2
TX36
BT12e1
80
35
2011
5
19
11
21:55
23:45
110
52.45
4.05
22
225
2
TX36
BT12e1
80
36
2011
5
19
11
23:55
01:55
120
52.36
4.07
22
225
2
TX36
BT12e1
80
37
2011
5
19
12
02:05
04:15
130
52.36
4.03
23
225
2
TX36
BT12e1
80
38
2011
5
19
12
04:25
06:30
125
52.3
3.59
20
225
2
TX36
BT12e1
80
39
2011
5
19
12
06:40
08:40
120
52.26
4.02
22
225
2
TX36
BT12e1
80
40
2011
5
19
12
08:50
10:40
110
52.26
4.02
21
315
2
TX36
BT12e1
80
41
2011
5
19
12
10:55
12:30
95
52.23
4.05
22
315
2
TX36
BT12e1
80
42
2011
5
19
12
12:40
14:20
100
52.24
3.55
22
315
3
TX36
BT12e1
80
43
2011
5
19
12
14:30
15:55
85
52.19
4.05
18
270
4
TX36
BT12e1
80
44
2011
5
19
12
16:05
17:50
105
52.27
3.55
21
270
4
TX36
BT12e1
80
45
2011
5
19
12
18:05
19:50
105
52.21
4.03
18
270
4
TX68
BT12e2
80
1
2011
5
19
9
02:00
03:45
105
52.5
4.07
22
270
1
TX68
BT12e2
80
2
2011
5
19
9
04:00
06:00
120
52.43
3.55
23
270
1
TX68
BT12e2
80
3
2011
5
19
9
06:15
07:45
90
52.36
3.41
25
270
1
TX68
BT12e2
80
4
2011
5
19
9
08:00
09:45
105
52.32
3.37
28
270
1
TX68
BT12e2
80
5
2011
5
19
9
10:00
11:30
90
52.3
3.36
28
270
1
TX68
BT12e2
80
6
2011
5
19
9
11:45
13:15
90
52.28
3.37
28
270
1
TX68
BT12e2
80
7
2011
5
19
9
13:30
15:00
90
52.24
3.38
27
270
1
TX68
BT12e2
80
8
2011
5
19
9
15:10
16:45
95
52.22
3.27
28
270
1
TX68
BT12e2
80
9
2011
5
19
9
17:05
18:35
90
52.2
3.13
30
270
1
Report number C122b/11
45 of 67
ship
gear
meshsize
haul
year
month
week
day
tset
thaul
duration
poslat
poslon
depth
winddir
windforc
TX68
BT12e2
80
10
2011
5
19
9
18:50
20:20
90
52.14
3.03
32
270
1
TX68
BT12e2
80
11
2011
5
19
9
20:35
22:10
95
52.08
2.56
30
270
1
TX68
BT12e2
80
12
2011
5
19
9
22:20
23:50
90
52.05
2.54
30
270
1
TX68
BT12e2
80
13
2011
5
19
10
00:05
01:50
105
52
3.05
30
270
1
TX68
BT12e2
80
14
2011
5
19
10
02:05
03:55
110
51.58
3.08
30
270
1
TX68
BT12e2
80
15
2011
5
19
10
04:10
06:00
110
51.56
3.07
30
270
1
TX68
BT12e2
80
16
2011
5
19
10
06:15
07:55
100
51.55
3.03
30
225
1
TX68
BT12e2
80
17
2011
5
19
10
08:10
09:45
95
51.55
3.02
30
135
1
TX68
BT12e2
80
18
2011
5
19
10
09:55
11:30
95
51.02
3.05
30
135
1
TX68
BT12e2
80
19
2011
5
19
10
11:45
13:15
90
52.09
3.11
30
135
1
TX68
BT12e2
80
20
2011
5
19
10
13:30
15:10
100
52.17
3.18
28
135
1
TX68
BT12e2
80
21
2011
5
19
10
15:35
17:10
95
52.18
3.3
26
135
1
TX68
BT12e2
80
22
2011
5
19
10
17:25
19:00
95
52.17
3.43
24
135
1
TX68
BT12e2
80
23
2011
5
19
10
19:15
21:00
105
52.2
3.49
23
135
1
TX68
BT12e2
80
24
2011
5
19
10
21:20
23:10
110
52.29
3.53
23
135
1
TX68
BT12e2
80
25
2011
5
19
10
23:25
01:15
110
52.27
3.53
23
135
1
TX68
BT12e2
80
26
2011
5
19
11
01:30
03:20
110
52.23
3.48
24
135
1
TX68
BT12e2
80
27
2011
5
19
11
03:40
05:40
120
52.21
3.5
24
135
1
TX68
BT12e2
80
28
2011
5
19
11
05:55
07:45
110
52.21
3.49
24
135
1
TX68
BT12e2
80
29
2011
5
19
11
08:05
10:00
115
52.22
3.4
24
135
1
TX68
BT12e2
80
30
2011
5
19
11
10:15
12:10
115
52.27
3.48
24
225
1
TX68
BT12e2
80
31
2011
5
19
11
12:25
14:00
95
52.36
3.55
23
270
1
TX68
BT12e2
80
32
2011
5
19
11
14:15
16:00
105
52.42
3.58
23
270
1
TX68
BT12e2
80
33
2011
5
19
11
16:20
18:00
100
52.51
4
24
270
1
TX68
BT12e2
80
34
2011
5
19
11
18:10
19:55
105
52.57
4.06
24
270
1
TX68
BT12e2
80
35
2011
5
19
11
20:05
21:40
95
52.51
4.08
23
270
1
TX68
BT12e2
80
36
2011
5
19
11
21:55
23:40
105
52.45
4.05
23
270
1
TX68
BT12e2
80
37
2011
5
19
12
23:55
01:55
120
52.37
4.01
24
270
1
TX68
BT12e2
80
38
2011
5
19
12
02:10
04:10
120
52.36
4.03
23
270
1
TX68
BT12e2
80
39
2011
5
19
12
04:25
06:30
125
52.28
4.06
22
270
1
TX68
BT12e2
80
40
2011
5
19
12
06:50
08:40
110
52.26
4.02
24
270
1
TX68
BT12e2
80
41
2011
5
19
12
08:55
10:30
95
52.25
4
23
270
2
TX68
BT12e2
80
42
2011
5
19
12
10:50
12:20
90
52.23
4.01
24
270
2
TX68
BT12e2
80
43
2011
5
19
12
12:35
14:05
90
52.24
3.55
23
270
2
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Report number C122b/11
ship
gear
meshsize
haul
year
month
week
day
tset
thaul
duration
poslat
poslon
depth
winddir
windforc
TX68
BT12e2
80
44
2011
5
19
12
14:20
15:50
90
52.21
4.02
24
270
2
TX68
BT12e2
80
45
2011
5
19
12
16:05
17:40
95
52.23
3.55
24
270
2
TX68
BT12e2
80
46
2011
5
19
12
17:55
19:35
100
52.23
4.01
23
270
2
TX68
BT12e2
80
47
2011
5
19
12
19:50
21:30
100
52.23
3.59
24
225
2
TX68
BT12e2
80
48
2011
5
19
12
21:50
23:50
120
52.24
4
24
225
2
Report number C122b/11
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Appendix C. Auction lists of the three vessels
ship
harbour
type
year
month
day
species
cat1
cat2
cat3
cat4
cat5
GO4
Scheveningen
auction
2011
5
13
PLE
258
507
640
1160
GO4
Scheveningen
auction
2011
5
13
SOL
155
239
238
364
295
GO4
Scheveningen
auction
2011
5
13
DAB
GO4
Scheveningen
auction
2011
5
13
TUR
39
20
22
22
61
GO4
Scheveningen
auction
2011
5
13
BLL
37
87
23
GO4
Scheveningen
auction
2011
5
13
COD
35
36
GO4
Scheveningen
auction
2011
5
13
WHG
GO4
Scheveningen
auction
2011
5
13
NEP
GO4
Scheveningen
auction
2011
5
13
VAR
cat6
tot
2565
1291
250
250
99
263
147
43
201
20
134
201
0
1769
1769
6620
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Report number C122b/11
ship
harbour
type
year
month
day
species
cat1
cat2
cat3
cat4
cat5
cat6
tot
TX36
IJmuiden
auction
2011
5
13
PLE
138
356
525
946
TX36
IJmuiden
auction
2011
5
13
SOL
150
268
198
328
236
TX36
IJmuiden
auction
2011
5
13
DAB
TX36
IJmuiden
auction
2011
5
13
TUR
29
21
28
32
55
TX36
IJmuiden
auction
2011
5
13
BLL
2
53
84
26
TX36
IJmuiden
auction
2011
5
13
COD
0
9
30
14
8
61
TX36
IJmuiden
auction
2011
5
13
WHG
4.4
2.2
0.5
0.0
0.0
7.0
TX36
IJmuiden
auction
2011
5
13
NEP
TX36
IJmuiden
auction
2011
5
13
VAR
1965
1180
200
200
78
243
165
0
16
104
56
573
34
44
827
4648
ship
harbour
type
year
month
day
species
cat1
cat2
cat3
cat4
TX68
Denhelder
auction
2011
5
13
PLE
121
379
493
1061
TX68
Denhelder
auction
2011
5
13
SOL
153
279
237
336
TX68
Denhelder
auction
2011
5
13
DAB
TX68
Denhelder
auction
2011
5
13
TUR
30
21
19
TX68
Denhelder
auction
2011
5
13
BLL
51
75
37
TX68
Denhelder
auction
2011
5
13
COD
0.0
2.7
21.4
TX68
Denhelder
auction
2011
5
13
WHG
TX68
Denhelder
auction
2011
5
13
NEP
TX68
Denhelder
auction
2011
5
13
VAR
cat5
cat6
tot
2054
249
1254
376
376
29
38
92
229
163
4.4
0.0
28.5
105
105
98
897
0
29
128
642
5107
Red numbers were reconstructed from the observation data on cod and whiting, and therefore not actually landed fish
Report number C122b/11
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Appendix D. Tables of observations on conditions of spine of filleted cod
Table 8-1: Observations of condition of spine of cod for GO4 catches (after trials in week 42, 2011)
No
Haul nr.
Length (cm)
spine fracture y/n
1
n/a
39.3
n
0
2
n/a
40.6
n
0
3
n/a
41
n
0
4
n/a
41.4
n
0
5
n/a
45.1
n
0
6
n/a
45.9
n
0
7
n/a
43.5
n
0
8
n/a
40.1
n
0
9
n/a
43.1
n
0
10
n/a
43.6
n
0
11
n/a
39.5
n
0
12
n/a
40.1
n
0
13
n/a
57.9
n
0
14
n/a
45.6
n
0
15
n/a
57.8
n
0
16
n/a
52.4
n
0
17
n/a
47.6
n
0
18
n/a
56.6
n
0
19
n/a
51.3
n
0
20
n/a
58.5
n
0
21
n/a
57.1
n
0
22
n/a
55.3
n
0
23
n/a
61.7
n
0
24
n/a
67.2
n
0
25
n/a
57.2
n
0
26
n/a
59.3
n
0
27
n/a
556.8
n
0
28
n/a
67.1
n
0
29
n/a
64.6
n
0
30
n/a
66.4
n
0
31
n/a
76.2
n
0
32
n/a
62.4
n
0
33
n/a
67.3
n
0
34
n/a
63.1
n
0
35
n/a
63.4
n
0
36
n/a
71.2
n
0
37
n/a
59.4
n
0
38
n/a
67.3
n
0
39
n/a
64.3
n
0
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Comments (photos)
Score
Report number C122b/11
No
Haul nr.
Length (cm)
spine fracture y/n
Comments (photos)
40
n/a
55.2
n
41
n/a
58.8
n
0
42
n/a
64.2
n
0
43
n/a
62.8
n
0
44
n/a
57.2
n
0
45
n/a
63.3
n
0
46
n/a
61.3
n
0
47
n/a
82.3
n
0
48
n/a
81.1
n
0
Blood stain near the tail
sum
Score
0
0
Spinal fracture in percentage
7.4%
Table 8-2: Observations of condition of spine of cod for TX36 catches
No
Haul nr.
Length (cm)
spine fracture y/n
Comments (photos)
Score
1
3
56
n
Lots of blood
0
2
3
62
n
Lots of blood
0
3
11
84
n
0
4
11
57
n
0
5
11
33
n
0
6
12
56
n
0
7
12
49
n
0
8
12
54
n
0
9
12
20
y
1
10
14
84
n
0
11
14
60
n
0
12
14
50
n
0
13
15
55
n
0
14
16
65
n
0
15
16
56
n
0
16
16
55
y
1
17
18
89
n
0
18
18
28
n
0
19
20
49
n
0
20
21
62
n
0
21
25
54
n
0
22
26
60
n
0
23
26
58
n
0
24
31
24
n
0
25
36
56
n
0
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26
37
54
n
0
27
37
56
n
0
sum
2
Spinal fracture in percentage
7.4%
Table 8-3: Observations of condition of spine of cod for TX68 catches
No
Haul nr.
Length (cm)
spine fracture y/n
Comments (photos)
Score
1
9
57
n
2
9
59
n
3
9
23
n
Badly filleted/ haemorrhages on left side
0
4
10
22
n
haemorrhages on left side
0
5
10
73
n
0
6
11
56
n
0
7
12
56
n
0
8
12
52
n
0
0
0
9
17
48
n
haemorrhages (unclear)
0
10
18
23
y
haemorrhages
1
11
18
27
y
haemorrhages
1
12
18
28
n
haemorrhages
0
13
18
58
n
0
14
18
58
n
0
15
20
66
n
0
16
21
56
n
0
17
29
58
n
18
40
56
n
haemorrhages
0
0
sum
2
Spinal fracture in percentage
11.1%
Table 8-4: Observations of condition of spine of whiting for TX36 catches
No
Haul nr.
Length (cm)
spine fracture y/n
Comments (photos)
Score
1
27
n
0
2
27
n
0
3
28
n
0
4
28
n
0
5
28
n
0
6
28
n
0
7
28
n
0
8
29
n
0
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Report number C122b/11
No
Haul nr.
Length (cm)
spine fracture y/n
Comments (photos)
Score
9
29
n
0
10
29
n
0
11
29
n
0
12
29
n
0
13
29
n
0
14
29
n
0
15
29
n
0
16
30
n
0
17
30
n
0
18
30
n
0
19
30
n
0
20
30
n
0
21
30
n
0
22
30
n
0
23
30
n
0
24
30
n
0
25
31
n
0
26
31
n
0
27
31
n
0
28
31
n
0
29
31
n
0
30
31
n
0
31
31
n
0
32
31
n
0
33
31
n
0
34
32
n
35
32
y
36
32
n
0
37
32
n
0
38
32
n
0
39
32
n
0
40
32
n
0
41
32
n
0
42
33
n
0
43
34
n
0
44
35
n
0
45
35
n
0
46
36
n
0
47
38
n
0
0
photo 134 + 135 = 1 fish
sum
Spinal fracture in percentage
Report number C122b/11
1
1
2.1%
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Appendix E. Digital photographs of filleted cod
GO4 Cod (week 42, 2011 after the trials)
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Figure 8-1: Digital photographs of filleted cod GO4
TX36 Cod
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Figure 8-2: Digital photographs of filleted cod TX36
TX36 Whiting
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Figure 8-3: Digital photographs of filleted whiting TX36
TX68 Cod
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Figure 8-4: Digital photographs of filleted cod TX68
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Appendix F. Raising procedures
From: van Helmond and van Overzee, 2008:
Table I. Explanation of the abbreviations used in the formulas this Appendix.
explanation
sub-
explanation
script
n
sampled number
l
length
N
total number
h
w
sampled weight
W
total weight
t
trip
v
sampled discards volume
p
period
V
total discards volume
y
year
u
sampled duration
s
species
U
total duration
f
fleet
wt
sampled landings weight
WT
total landings weight
e
sampled fleet effort in number of trips
E
total fleet effort in number of trips
T
Number of trips
DN
total discard number
LN
total landings number
CN
total catch number (landings and discards
haul
hour
o
combined)
Raising discards per trip
The sampled number per length and haul were raised per species to total number per length and haul
DNl , h, s 
Vh
Dnl , h, s
vh
where DNl,h,s is the total number discarded at length (l) in haul (h) for species (s), Vh is total volume of
haul (h), vh is sampled volume of haul (h) and Dnl,h,s sampled number discarded at length (l) in haul (h)
for species (s).
The total number discarded at length per haul and species was summed over the sampled hauls to obtain
the total sampled number discarded at length (l) for species (s) over all sampled hauls (h). The total
number discarded (DNl,t,s) at length (l) per trip (t) and species (s) was calculated by multiplying the total
number discarded (DNl,h,s) over all sampled hauls with the ratio of total trip duration (Ut) and duration of
all sampled hauls (Σuh):
DNl ,t , s 
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Ut h
 DNl ,h, s
 uh h  i
Report number C122b/11
The number discarded at length per hour and species (DNl,o,t,s) was calculated by dividing the total
number at length per trip (DNl,t,s) by total trip duration (Ut).
DNl , o,t , s 
DNl ,t , s
Ut
The obtained number discarded at length per hour (DNl,o,t,s) was summed over length to obtain the
number discarded per hour (DNo,t,s):
DNo,t , s   DNl , o,t , s
l i
Discarded weight per hour per species at length was calculated using length-weight relationships:
DWl , o,t , s
 DNl , o,t , s * As * l Bs 

  

Ut
l 

where DWl,o,t,s is the weight per length, per hour and per species, DNl,o,t,s is the number discarded at
length, per hour and per species and As and Bs species specific constants.
Raising landings per trip
The sampled number landed at length per haul and species (Lnl,h,s) were summed over all sampled hauls
(h) to calculate the sampled number at length for the trip (nl,t,s). The total number landed at length for
the entire trip (LNl,t,s) was calculated by multiplying the sampled number at length for the trip (Lnl,t,s)
with the ratio of total trip weight obtained from auction or VIRIS data (WTt,s) to sampled landings weight
of the trip (wtt,s):
LNl ,t , s 
WTt , s  h

  Lnl , h, s 
wtt , s  h  i

Number landed at length per hour per species (LNl,o,t,s) was calculated by dividing total number landed at
length per trip (LNl,t,s) by the trip duration (Ut).
LNl , o ,t , s 
LNl ,t , s
Ut
The obtained total number at length per hour (LNl,o,t,s) was summed to calculate number per hour per
species (LNo,t,s):
LNo,t , s   LNl , o,t , s
l i
Total landings weight per hour (LWo,t,s) was calculated per species by dividing total landings weight
(WTt,s) per species by total trip duration (Ut).
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LWo,t , s 
WTt , s
Ut
Numbers at length, per quarter and year
The number of discards and landings (CNl,o,p,s) at length per hour was calculated per quarter/year by
summing the number landings or discards at length per hour per trip (CNl,o,t,s) over all trips in that period
(p) and then dividing this by the total number of trips (Ut) in this period:
CN l ,o, p ,s  ( CN l ,o,t ,s ) / U t
p
p
Total numbers discards or landings (CNo,p,s) were calculated by summing over length. Trips were
excluded from calculation numbers per hour per period if landings were not measured during a trip, but
auction records existed for this species.
CN o, p ,s   CN l ,o, p ,s
l i
Numbers at age, per quarter and year
The age structure of both plaice and sole discard and landings was calculated by distribution of numbers
at length over age groups using age-length-keys (ALK). The number landed and discarded (CNl,a,t,s) at
length and age per trip and species was calculated by distribution of the proportion (fl,a ) of fish at length
(l) with age (a) over the number (CNl,t,s) at length per trip and species. Because fl,a is dependent on the
period, ALK were taken from discards and market samples from the quarter were discards were sampled.
CNl , a,t , s  fl , a * CNl ,t , s
The number landed and discarded (CNa,t,s) at age per trip and species was calculated by multiplying the
number landed and discarded (CNl,a,t,s) at length and age per trip and species over length:
CN a ,t , s   CNl , a ,t , s
l i
The number of discards and landings (CNa,o,p,s) at age per hour was calculated per quarter/year by
summing the number of landings or discards at age per hour per trip (CNa,o,t,s) over all trips in that period
(p) and then dividing this by the total number of trips (Ut) in this period:
CN a ,o, p ,s  ( CN a ,o,t ,s ) / U t
p
p
Numbers at age, per quarter and year per fleet
Total landings en discards (CNa,p,s,f) at age per quarter/year were calculated for the entire fleet by
multiplying the total numbers of discards and landings (Na,p,s) at age per quarter/year with the ratio
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Report number C122b/11
effort of the entire fleet (Ep,f) per quarter/year measured in Hpeffort (proportion fishing duration per day
multiplied with engine power) to the effort of the sampled part of the fleet in Hpeffort per quarter (ep,f).
CN a , p , s , f 
E p, f
ep, f
CN a , p , s
Trips were excluded from calculation numbers per hour per period if landings were not measured during
a trip, but auction records existed for this species.
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